1. Field of the Invention
The present invention relates to a vinylidene fluoride resin composition and a resin film, a back sheet for solar cells, and a solar cell module comprising the resin composition. More specifically, it relates to a technology for preventing discoloration of resin films for use in applications demanding weather resistance, such as solar cell modules.
2. Description of the Related Art
Various natural energies have been used more frequently recently for reduction of release of carbon dioxide to overcome the problem of global warming and, in particular, solar cells that utilize solar energy are attracting attention. However, solar cell modules, which are used outdoors for an extended period of time, have to satisfy stricter requirement on durability. Thus, the solar cells generally have a structure in which they are sealed with a thermoplastic resin such as an ethylene vinyl acetate copolymer (EVA) resin and held additionally as protected between glass on the sunlight-incoming face and a back sheet on the other face.
Vinylidene fluoride resins superior in mechanical strength, chemical resistance, and weather resistance are attracting attention as the weather-resistant resin film materials for preparation of the back sheets for protection of the rear-face of the solar cell modules. And, a solar cell module having a laminate film of a vinylidene fluoride resin film and a polyethylene terephthalate film as the back sheet and a solar cell module having a laminate film of a transparent highly moisture-proof film with an inorganic oxide coated thereon have been proposed (see, for example, Patent Documents 1 and 2).
The back sheet is formed as the lowest layer in the solar cell module for protection of the solar cell and its wiring, and a white sheet is occasionally used, in addition for the protection described above, for improvement of reflectance of sunlight and thus of power-generating efficiency of the solar cell module (see, for example, Patent Documents 3 and 4). Such a white vinylidene fluoride resin film is prepared, for example, by blending a white pigment such as titanium oxide to a vinylidene fluoride resin composition and filming the blend.